The present invention relates to surface inspection apparatus and methods for optically detecting defects present on a surface of a semiconductor substrate or the like and identifying respective types of the detected defects, and more particularly to an improved surface inspection apparatus and method which can distinguish, with an increased accuracy, between different types of defects present on a surface of a semiconductor wafer or the like, e.g., between foreign substances and crystal-originated pits or between foreign substances and scratches.
Generally, semiconductor wafers are made of high-purity polycrystalline silicon. Because the quality of the semiconductor wafer is greatly influenced by defects on the wafer surface, it has been conventional to carefully inspect the wafer surface using a surface inspection apparatus. Examples of the defects produced on the wafer surface include minute foreign substances such as dusts or polishing material or slurry adhered to the wafer surface, crystal-originated defects such as crystal-originated particles and pits, and scratches caused by surface polishing operations (polishing scratches). The crystal-originated pits (also known as xe2x80x9cCOPsxe2x80x9d) are produced in the wafer surface by minute oxidized silicon particles, formed on the wafer surface as a result of silicon atom oxidization, being caused to peel off the wafer surface due to the wafer surface polishing. The polishing scratches are formed as minute lines on the wafer surface.
To detect such various defects on and in the wafer surface, some of the conventional surface inspection apparatus use an optical defect detection method, in accordance with which a laser light beam is projected or irradiated onto the wafer surface and surface defects are detected by receiving reflected and scattered lights, from the wafer surface, of the laser light beam to examine optical characteristics of the received reflected and scattered lights that depend on shapes, sizes, etc. of possible defects on the wafer surface.
One example of the conventionally-known surface inspection apparatus for detecting foreign substances and crystal-originated pits present on and in the wafer surface is disclosed in Japanese Patent Laid-open Publication No. HEI-9-304289. The disclosed surface inspection apparatus is arranged to determine there is a foreign substance on the wafer surface when scattered lights, from the wafer surface, of the laser light beam projected or irradiated onto the wafer surface have been received by both of a low-angle photodetector (i.e., light receiving element) and medium-angle photodetector and determine that there is a crystal-originated pit in the wafer surface when a scattered light of the laser light beam has been received by only the medium-angle photodetector.
There has also been known another type of the surface inspection apparatus for detecting foreign substances and crystal-originated pits present on and in the wafer surface, which is arranged to determine that there is a foreign substance on the wafer surface when scattered lights, from the surface, of the laser light beam irradiated onto the wafer surface have been received by both of a high-angle photodetector and medium-angle photodetector and determine that there is a scratch on the wafer surface when a scattered light of the laser light beam has been received by only a low-angle photodetector.
Crystal-originated pits of various sizes and shapes tend to be produced in the wafer surface, because the depths and diameters of the pits differ depending on the extent with which the individual oxidized silicon particles peeled off the wafer surface. Therefore, with some crystal-originated pit having a particular shape, the lights, which should normally be scattered toward the medium-angle photodetector with predetermined directivity, may also be scattered with directivity in another direction. In such a case, not only the medium-angle photodetector but also the low-angle photodetector in the above-mentioned conventional surface inspection apparatus would undesirably detect the scattered lights caused by the crystal-originated pit, so that the crystal-originated pit would be erroneously detected as a foreign substance.
Also, scratches of various sizes and shapes tend to be produced on the wafer surface. Therefore, with some scratch having a particular shape, the lights, which should be scattered toward the low-angle photodetector with predetermined directivity, may also be scattered with directivity in another direction. In such a case, not only the low-angle photodetector but also the medium and high-angle photodetectors in the second-mentioned conventional surface inspection apparatus would detect the scattered lights caused by the scratch, so that the scratch would be erroneously detected as a foreign substance.
It is therefore an object of the present invention to provide a surface inspection apparatus and method which can distinguish, with a high accuracy, between a foreign substance and a crystal-originated pit on and in a substrate surface to be inspected.
It is another object of the present invention to provide a surface inspection apparatus and method which can distinguish, with a high accuracy, between a foreign substance and a scratch on a substrate surface to be inspected.
According to one aspect of the present invention, there is provided an improved surface inspection apparatus which comprises: an optical system that irradiates a light beam onto a surface of a substrate to be inspected and receives scattered lights from the surface of the substrate at different light reception angles, to thereby generate first and second light detection signals corresponding to the different light reception angles; and a processing device that sets a reference function defining correlations in level value between the first and second light detection signals, makes a comparison between respective level values of the first and second light detection signals using the reference function as a comparison reference, and determines, on the basis of a result of the comparison, which of a plurality of different types of defects a possible defect present on the surface of the substrate, represented by the light detection signals, corresponds to. With the inventive arrangements that the level values of the first and second light detection signals output from the optical scanning system are compared by use of the reference function defining the correlations in level between the first and second light detection signals and a determination is made, on the basis of the result of the comparison, as to which of the plurality of different types of defects a detected possible defect present on the surface of the substrate (e.g., semiconductor wafer) corresponds to, the present invention achieves a high-accuracy distinction between any foreign substances and crystal-originated pits present on and in the substrate surface.
According to another aspect of the present invention, there is provided a surface inspection apparatus which comprises: an optical system that irradiates a light beam onto a surface of a substrate to be inspected and receives scattered lights from the surface of the substrate at different light reception angles, to thereby generate a plurality of light detection signals corresponding to the different light reception angles; and a processing device that weights a level value of a predetermined one of the light detection signals with a predetermined coefficient, makes a comparison between the weighted level value of the predetermined light detection signal and a level value of the remaining light detection signal, and identifies, on the basis of a result of the comparison, any of a plurality of different types of defects present on the surface of the substrate. In the present invention, the level value of the predetermined light detection signal from among the plurality of light detection signals is weighted with the predetermined value to thereby differentiate the thus-weighted level of the light detection signal from the level of the remaining light detection signal (i.e., exaggerate the level difference between the predetermined light detection signal and the remaining light detection signal), so that identification operations optimal for each type of defect to be identified can be facilitated. Thus, by determining which one of the weighted level of the predetermined light detection signal and level of the remaining light detection signal is greater than the other, the present invention achieves a high-accuracy distinction between a foreign substance and a scratch present on the substrate surface.
The present invention may be constructed and implemented not only as the apparatus invention as discussed above but also as a method invention. Also, the present invention may be arranged and implemented as a software program for execution by a processor such as a computer or DSP, as well as a storage medium storing such a program. Further, the processor used in the present invention may comprise a dedicated processor with dedicated logic built in hardware, not to mention a computer or other general-purpose type processor capable of running a desired software program.
While the described embodiments represent the preferred form of the present invention, it is to be understood that various modifications will occur to those skilled in the art without departing from the spirit of the invention. The scope of the present invention is therefore to be determined solely by the appended claims.